Question

Identify the correct option
According to $CIP$ sequence rule, the correct arrangement in order of decreasing priority is:
A. $- OH > C{H_2}OH > - CHO > - COOH$
B. $- OH > COOH > - CHO > - C{H_2}OH$
C. $- COOH > OH > - COH > - C{H_2}OH$
D. $COOH > - CHO > - C{H_2}OH > - OH$

Answer 1

The higher the atomic number of the immediate substituent atom, the higher the priority.
For example:
$H - < C - < N - < O - < Cl -$

Complete step by step answer:
-The $CIP$ rule is a standard process used in organic chemistry to completely and unequivocally name a stereoisomer of a molecule.
-Priority is numerically assigned as $1,2,3$ and $4$ where smaller the number higher will be the priority. So, $1$ has the highest priority and $4$ has the lowest priority.
Rules for giving the priority:
Rule$1$: Atoms having greater atomic number is given more priority
$- OH \Rightarrow \,\,{\text{First}}$
Atomic number of ${\text{0}}$ is $8$.
Rule $2$: If ${1^{st}}$ atom is the same then, see ${2^{nd}}$ atom and apply Rule $1$.
Rule $3$: For multiple bond
I
II
Break multiple bonds and add one more same atom to that. After this apply Rule$1$ and Rule $2$.
So, the answer is $- OH > COOH > - CHO > - C{H_2}OH$
This is the decreasing priority order.
Multiple bonds are treated as separate single bonds.

Note: $- CH = O$ is given priority over $- C{H_2}OH$
$I > Br > Cl$
$OH > N{O_2} > N{H_2} > COOH > CHO > C{H_2}$
In geometric isomers:
$Z - {\text{isomer > }}E - {\text{isomer}}$